The invention relates to treatment methods of glow-discharge plasma near the atmospheric pressure and apparatus thereof.
Surface modification or treatment by applying glow-discharge plasma under a low pressure is known and has been practiced. However, the treatment under a low pressure is not advantageous for commercial application and has to be limited to the treatment of highly priced parts, such as electronic devices. More advantageous treatment methods which involve in discharging plasma near the atmospheric pressure have been proposed. For example, U.S. Pat. No. 5,126,164 discloses methods to treat in the atmosphere of helium gas, and U.S. Pat. No. 5,124,173 discloses methods to treat in the atmosphere of argon plus acetone and/or helium.
These methods are restrictive due to the fact that they require to generate plasma in an atmosphere containing helium or acetone as the essential component. The process will be commercially disadvantageous because of the high price of helium. Acetone can primarily be used in a hydrophilic treatment, because it would react with the surface being treated and give a hydrophilic finish.
U.S. Pat. No. 5,529,631 discloses an art of continuous web treatment under the atmospheric pressure in which air in the treating chamber is replaced by a desirable gas, such as helium, which is then continually supplied during the operation and the web is treated in this loosely sealed treating chamber where the discharge-plasma is provided. However, when the line speed exceeds 3 m/min in this process, air is engulfed into the chamber and disturbs the electric discharge to make it difficult to obtain the expected result.
It is an object of the invention to provide a stable method and an apparatus for surface treatment by electric discharge-plasma that is generated near or around the atmospheric pressure.
It is another object of the invention to provide an effective method of plasma treatment for a wide range of gas atmosphere.
It is a further object of the invention to provide a method and an apparatus of a glow-discharge plasma treatment for a continuously running web at a fast speed near the atmospheric pressure.